Evaluate options for reducing the overall volume of wastewater generated and the total dissolved solids (TDS) so that production can be increased while complying with anticipated permit limits at a specialty metals processing plant site.
The client, a specialty metals manufacturer in the northeastern United States, currently treats all its process wastewater using chemical treatment/neutralization (lime and sulfuric acid), precipitation, and filtration in its Wastewater Treatment Process (WWTP). The client’s existing NPDES permit regulates total flow and constituent mass loadings and concentrations at the discharge outfall. The client anticipates a potential increase in production resulting in an increase in the total volume of wastewater produced and subsequently total mass loadings at the outfall. In addition, it is also anticipated that the total dissolved solids (TDS) discharge limits in the existing permit may be reduced with future permit modifications or renewal. Therefore, the client contracted with Process Engineering Associates, LLC (PROCESS) to evaluate options for reducing the overall volume of wastewater generated and the TDS so that production can be increased while complying with anticipated permit limits. The evaluation had to take into consideration how the reduction in TDS and overall volume would impact all of the other constituent limits in the existing permit.
PROCESS first generated a material balance model that reflected the existing wastewater treatment system using data provided by the client with estimated average and peak flow rates, as well as the estimated constituent concentrations at each major process area source. The model was validated using actual process data. PROCESS then evaluated the following treatment methods for reducing the hydraulic loading and TDS loading:
- Mechanical Vapor Compression (MVC) – evaluated for two specific high-TDS concentration wastewater streams; both separately and as a combined option
- Carrier Gas Extraction (CGE) – evaluated for two specific high-TDS concentration wastewater streams; both separately and as a combined option
- Cost Effective Sulfate Removal (CESR) – evaluated as an additional chemical treatment step using an aluminum-oxide based reagent to form an ettringite solid to precipitate soluble sulfates
- Replacement of Sulfuric Acid with Carbon Dioxide (CO2) – evaluated in existing treatment process to minimize the formation of soluble sulfates
- Reverse Osmosis (RO) – evaluated as an end-of-pipe option for removal of TDS from the final treated wastewater stream.
For each alternative, a heat and material balance (HMB) and Block Flow Diagram (BFD) were developed as well as budget level capital (CAPEX) and operating (OPEX) cost estimates. The alternatives were compared based on their projected level of expected TDS reduction (and subsequent allowable production capacity increase), proven performance with past installations, required additional testing, and estimated CAPEX and OPEX projections.
In addition to the treatment alternatives evaluation, PROCESS also used the model to evaluate expected total hydraulic loading at key points in the existing wastewater treatment system and total TDS concentration at the outfall at various increased production capacities assuming no additional treatment methods were implemented. This allowed the client to gain a better understanding of potential equipment limitations that may exist as production ramped up.
It was determined that peak production capacity could be achieved using MVC or similar technology on the combined high-TDS wastewater streams. The client is moving forward with treatability testing for one or more of the other options to validate estimated TDS reduction levels. In addition, it was also determined that the hydraulic capacity of the existing WWTP equipment would not be exceeded at peak production capacities assuming adequate upstream equalization was available which the client is working to validate as well.
Specialty Metals Manufacturing
- Industrial wastewater treatment design
- Process alternatives evaluations
- CAPEX and OPEX estimation.